Medical treatment of several illnesses requires continuous drug infusion into various body compartments, such as subcutaneous and intra-venous injections. Diabetes mellitus (DM) patients, for example, require the administration of varying amounts of insulin throughout the day to control their blood glucose levels. In recent years, ambulatory portable insulin infusion pumps have emerged as a superior alternative to multiple daily syringe injections of insulin, initially for Type 1 diabetes patients and consecutively for Type 2 diabetes patients. These pumps, which deliver insulin at a continuous basal rate as well as in bolus volumes, were developed to liberate patients from repeated self-administered injections and allow them to maintain a near-normal daily routine. Both basal and bolus volumes must be delivered in precise doses, according to individual prescriptions, since an overdose or under-dose of insulin could be fatal.
The first generation of portable insulin pumps involves a “pager-like” device with a reservoir contained within a housing. The reservoir is typically a syringe barrel and drug is delivered by a continuous forward motion of a plunger within the barrel. Examples of such devices are disclosed in U.S. Pat. Nos. 6,248,093 and 7,390,314. In a typical configuration known in the art, a motor rotates a gear that rotates a drive screw. The plunger is comprised of a proximal end (“plunger head” or “piston head”) that contains gaskets and an elongated member shaped like a longitudinal segment of a cylinder (“plunger member”) which is internally threaded so that it is inserted into a position of engagement with the drive screw. The drive screw is a threaded screw gear having a diameter that meshes with the internal threads of the plunger member. Thus the motor rotates the drive screw, which engages the threads of the plunger member to displace the plunger in a linear direction. One skilled in the art will understand that the “plunger member” with internal threads is basically a plunger nut. Rotating the drive screw within the plunger nut converts the rotational motion of the drive screw into linear motion of the plunger. While these first generation “pager-like” devices represent a significant improvement over multiple daily injections, they suffer major drawbacks, including large size and weight and long tubing.
To avoid such limitations, a new concept was proposed and implemented in second generation pumps. The new concept concerns a remote-controlled skin-adherable device having a bottom surface adapted to be in contact with the patient's skin. A reservoir is contained within the housing and reservoir filling is done with an additional syringe that is used to draw the drug from a vial with an injection needle that is also adapted for fluid communication with the reservoir. This paradigm was discussed, for example, in U.S. Pat. Nos. 4,498,843, 5,957,895, 6,589,229, 6,740,059, 6,723,072 and 6,485,461. These second generation skin-adherable devices also have drawbacks, the most significant being that the entire device, including all the expensive components (e.g., electronics and driving mechanism), must be disposed every 2-3 days due to, for example, insertion site infections and reduced insulin absorption.
A typical driving mechanism of a second generation, skin-adherable pump is described in U.S. Published Patent Application No. 2005/0238507 assigned to Insulet Corporation. Insulet's device has a plunger rigidly connected to a non-rotating threaded drive screw and is coupled to a drive wheel that includes a thread-engaging mechanism that moves from a non-thread-engaging position to a thread-engaging position. The non-thread-engaging position allows the threaded drive screw to pass freely through the drive wheel when the reservoir is being filled. The thread-engaging position allows the threaded drive screw to be advanced when the drive wheel is rotated.
Third generation skin-securable devices were devised to avoid the cost issues (e.g., disposing expensive components every 2-3 days) of the second generation devices and to extend patient customization. An example of such a device is described in co-owned U.S. patent application Ser. No. 11/397,115 (Publication No. 2007/0106218), filed Apr. 3, 2006 and entitled “Systems and Methods for Sustained Medical Infusion and Devices Related Thereto” and International Patent Application No. PCT/IL06/001276 (Publication No. WO/2007/052277), filed May 11, 2006 and entitled “Modular Portable Infusion Pump.” This third generation device contains a remote control unit and a skin-securable (e.g., adherable) unit (e.g., “patch unit”) that includes two parts: (1) a reusable part containing the electronics, at least a portion of the driving mechanism and other relatively expensive components, and (2) a disposable part containing the reservoir.
A skin-securable fluid (e.g., insulin) delivery device was also disclosed in co-owned U.S. patent application Ser. No. 11/989,681 and International Patent Application No. PCT/IL07/000,932 (Publication No. WO/2008/012817), both filed Jul. 24, 2007, claiming priority to U.S. Provisional Patent Application Nos. 60/833,110 filed Jul. 24, 2006 and 60/837,877 filed Aug. 14, 2006, and entitled “Systems, Devices, and Methods for Fluid/Drug Delivery,” the content of all of which is incorporated herein by reference in its entirety.
A typical driving mechanism of a third generation skin-securable pump is described in U.S. Published Patent Application No. 2008/0097327 assigned to Medtronic MiniMed. The disposable part in this pump includes a plunger having a rigidly-connected drive screw. The reusable part contains a motor and a gear that comprises a driving wheel. Upon connection of reusable and disposable parts, the drive screw is engaged with the drive wheel. Rotation of the drive wheel is converted to linear motion of the drive screw.
A fourth generation infusion device has been devised as a dispensing unit that can be disconnected from and reconnected to a skin-securable cradle unit and can be operated by buttons located on the reusable part. This fourth generation device is disclosed in the following co-owned applications: (i) U.S. patent application Ser. No. 12/004,837 (Publication No. 2008/0215035) and International Patent Application No. PCT/IL07/001578 (Publication No. WO2008/078318), both filed Dec. 20, 2007, claiming priority to U.S. Provisional Patent Application No. 60/876,679 filed Dec. 22, 2006, and entitled “Systems, Devices, and Methods for Sustained Delivery of a Therapeutic Fluid,” (ii) International Patent Application No. PCT/IL08/001001 (Publication No. WO2009/013736), filed Jul. 20, 2008, claiming priority to U.S. Provisional Patent Application No. 60/961,527 and entitled “Manually Operable Portable Infusion Pump” and (iii) International Patent Application No. PCT/IL08/001057 (Publication No. WO2009/016636), filed Jul. 31, 2008, claiming priority to U.S. Provisional Application Nos. 60/963,148 and 61/004,019, and entitled “Portable Infusion Device with Means for Monitoring and Controlling Fluid Delivery,” the content of all of which is incorporated herein by reference in its entirety.
The third and fourth generation devices can be used in conjunction with an analyte (e.g., glucose) sensing apparatus to enable continuous readings of analyte levels. Fluid dispensing can be done automatically according to analyte sensing (closed loop system) or semi-automatic if the user wishes to control delivery (open loop system). A fourth generation device with sensing capabilities is disclosed in the co-owned U.S. patent application Ser. Nos. 11/706,606 (Publication No. 2007/0191702), filed Feb. 14, 2007 and entitled “Systems and Methods for Sensing Analyte and Dispensing Therapeutic Fluid,” and 11/963,481 (Publication No. 2008/0214916), filed Dec. 21, 2007 and entitled “Fluid Delivery with In Vivo Electrochemical Analyte Sensing,” the content of all of which is incorporated herein by reference in its entirety.
A typical pumping mechanism of third and fourth generation two-part skin-securable devices may be a “syringe-like” or “piston-type” pumping mechanism. Here, a plunger (e.g., piston) slides within a reservoir (e.g., barrel) to draw fluid outwardly. The plunger may be pushed forward by a rotating drive screw (plunger rod) that freely articulates within the plunger. Linear motion is achieved by rotation of the drive screw relative to a nut. The nut is rigidly fixed to the housing or chassis (insert) of the disposable part. Rotating the drive screw within the non-rotating nut causes linear motion of the drive screw relative to the nut. The drive screw is also used as a plunger rod to backwardly slide the plunger during reservoir filling. After filling, the disposable part that contains the reservoir and outlet port is connected to the reusable part concomitantly with engagement of the drive screw with the gear of the reusable part.
The major limitation of a freely-articulating rotating drive screw is inaccuracy in drug delivery caused mainly due to plunger wobbling during forward motion within the reservoir. Plunger wobbling is caused by rotation of the distal end of the drive screw at the articulation point within the plunger.